The invention is an improvement in the invention disclosed in my pending patent application entitled "POWERTRAIN ASSEMBLY WITH CROSS-AXIS DISPOSITION OF THE ENGINE CRANKSHAFT AND THE TRANSMISSION TORQUE INPUT SHAFT", which was filed Jan. 29, 1990, Ser. No. 471,759.
The invention of my copending application, which is assigned to the assignee of this invention, is adapted particularly to be used in a front-wheel drive vehicle in which the axis of the internal combustion engine is mounted in the direction of the vehicle center plane in a fore-and-aft direction. Multiple ratio transmission gearing is arranged with the axis of the gearing disposed perpendicularly with respect to the axis of the engine crankshaft to form a T-drive configuration. This makes it possible to design the transmission and engine package with minimum space requirements, thereby improving the styling options for the vehicle designer and reducing the intrusion of the engine and transmission assembly into the passenger and cargo space for the vehicle.
Because of the reduced powertrain dimensions made possible by such a T-drive configuration, the vehicle exterior size can be reduced, which results in weight reduction, a reduction in the number of components, and reduced manufacturing cost.
The T-drive configuration of the invention described in my copending application is achieved by locating an engine crankshaft gear at a mid-crankshaft position on a nodal point for torsional vibrations in the crankshaft. This divides the crankshaft effectively into two crankshaft portions, each of which has its own natural torsional frequency. The amplitudes of the torsional vibrations that occur in the crankshaft are reduced substantially because of the strategic position of the engine crankshaft gear.
The engine dynamic forces that are transmitted to the crankshaft and the loading on the gear that results from the engine firing forces and torques have a minimal effect on the gear tooth loading.
A T-drive arrangement of the kind described in my copending patent application is unlike other transaxle arrangements presently used in the automotive industry, such as the transaxle described in U.S. Pat. Nos. 4,509,389 and 4,368,649, each of which is assigned to the assignee of my invention. In the case of the drivelines described in these prior art references, the engine crankshaft axis is arranged transversely with respect to the vehicle center plane rather than in the fore-and-aft direction, as in the case of the present invention. Further, the torque output shaft for the transmission gearing is arranged in spaced, parallel relationship with respect to the crankshaft axis.
The crankshaft gear in the powertrain assembly of my copending application engages a transmission torque input gear. The gear teeth for each of the gears are beveled so that the axis of the transmission torque input gear and the crankshaft axis are perpendicular, one with respect to the other. One of the possible drawbacks for cross-axis gearing of this kind is the tendency for the cross-axis gears to emanate an undesirable noise because of variations in the tooth geometry for the meshing gear teeth. Furthermore, the crankshaft gear itself is subjected to unusual forces because of firing forces of the engine and severe transient torque fluctuations that occur in the direct-driving connection between the crankshaft and the transmission input gearing. Some of the undesirable gear noise, sometimes referred to as gear rattle, is caused by backlash between meshing gear teeth of the crankshaft gear and the torque input gear for the transmission. Further, the severe forces applied to the gears, because of transient torque fluctuations and engine firing forces tend to reduce the durability of the driving connection between the transmission input gear and the transmission input shaft itself.
If the connection between the input shaft and the transmission torque gear input is a spline connection, it is possible that the unusual forces that are transmitted through the gearing will cause failure of the spline teeth. If the driving connection is established by a keyway, it is possible that the unusual forces transmitted through the gearing will destroy the key. In either case, the overall durability of the powertrain is reduced.